In video system applications, a picture is displayed on a television or a computer screen by scanning an electrical signal horizontally across the screen one line at a time using a scanning circuit. The amplitude of the signal at any one point on the line represents the brightness level at that point on the screen. When a horizontal line scan is completed, the scanning circuit is notified to retrace to the left edge of the screen and start scanning the next line provided by the electrical signal. Starting at the top of the screen, all the lines to be displayed are scanned by the scanning circuit in this manner. A frame contains all the elements of a picture. The frame contains the information of the lines that make up the image or picture and the associated synchronization signals that allow the scanning circuit to trace the lines from left to right and from top to bottom.
There may be two different types of picture or image scanning in a video system. For some television signals, the scanning may be interlaced video format, while for some computer signals the scanning may be progressive or non-interlaced video format. Interlaced video occurs when each frame is divided into two separate sub-pictures or fields. These fields may have originated at the same time or at subsequent time instances. The interlaced picture may be produced by first scanning the horizontal lines for the first field and then retracing to the top of the screen and then scanning the horizontal lines for the second field. The progressive, or non-interlaced, video format may be produced by scanning all of the horizontal lines of a frame in one pass from top to bottom.
In video compression, communication, decompression, and display, there has been for many years problems associated with supporting both interlaced content and interlaced displays along with progressive content and progressive displays. Many advanced video systems support either one format or the other format. As a result, deinterlacers, devices or systems that convert interlaced video format into progressive video format, have become an important component in many video systems.
However, deinterlacing takes fields from interlaced video and coverts them into frames of progressive video, at double the display rate. Certain problems may arise concerning the motion of objects from image to image during deinterlacing. Objects that are in motion are encoded differently in interlaced fields and progressive frames. Video images or pictures, encoded in interlaced video format, containing little motion from one image to another may be de-interlaced into progressive video format with virtually no problems or visual artifacts. However, visual artifacts become more pronounced with video images containing a lot of motion and change from one image to another, when converted from interlaced to progressive video format. As a result, some video systems were designed with motion adaptive deinterlacers.
Areas in a video image that are static are best represented with one approximation. Areas in a video image that are in motion are best represented with a different approximation. A motion adaptive deinterlacer attempts to detect motion so as to choose the correct approximation in a spatially localized area. An incorrect decision of motion in a video image results in annoying visual artifacts in the progressive output thereby providing an unpleasant viewing experience. Several designs have attempted to find a solution for this problem, but storage and processing constraints limit the amount of spatial and temporal video information that may be used for motion detection.
Frame rate defines how many pictures or frames of video information are displayed per second and the general units are frames per second (fps). In general, movies are shot at a frame rate of 24 fps. However, the standard promulgated in the United States by the National Television System Committee (NTSC) requires that information be displayed at a frame rate of 29.97 fps. Accordingly, the frame rate of movies shot at 24 fps must be changed in order to for them to be correctly displayed on NTSC compliant televisions. This process of changing the frame rate of movies from 24 fps to 29.97 fps is called telecine. Inverse telecine (IVTC) is the process utilized to transform movies from NTSC's frame rate of 29.97 fps back to a frame rate of 24 fps.
In displaying video on a screen, horizontal lines are displayed from top to bottom. A signal traces the display of the horizontal like from top to bottom of the screen. In old displaying devices, the tracing signal would take time to return to the top of the screen, to begin scanning again. The time it takes the tracing signal to get from the bottom of the screen to the top is called vertical blanking. These days, during the vertical blanking intervals, information may be inserted about the video such as, for example, whether text is added to the video (closed captioning and teletext), modes of display (widescreen mode, etc.), and other similar display-related information.
So in systems that use deinterlacers, the system detects pixels coming through the deinterlacer, and generates statistics on them to perform 3:2 pulldown or 2:2 pulldown. Problem may arise during blanking intervals, because when they go through the system, and they have nothing to do with the video itself, the information that is not relevant to the video information and pixels, may cause problems for the system that is looking for a 3:2 or 2:2 pattern.
If used, the data present within a vertical blanking interval of video can significantly affect the accuracy of one or more statistical measures used by a video processing system, such as an inverse telecine deinterlacing system that performs reverse 3:2 or 2:2 pull-down of video. The statistical measures may be utilized by a video system to handle discrepancies. Some statistical measures that are negatively affected when data resident in vertical blanking intervals is utilized, are frame-based statistical measures. A frame-based statistical measure may utilize all pixels in the frame, including those pixels resident within vertical blanking intervals.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.